The present invention relates to a driving system for an electrochromic display device which includes an electrochromic material held in two electrode carrying support plates to manifest reversible variations in the light absorption properties when current is supplied.
Generally, there are two types of electrochromic displays (ECD). The first type of ECD utilizes an electrically-induced chemical reduction of a colorless liquid to produce a colored, insoluble film on an electrode surface. The second type of ECD employs an inorganic solid film formed on electrodes, wherein the color variation is produced by the change in the opacity of the inorganic solid film.
The inorganic solid film used in the second type of ECD is the film of the transition metal oxide material such as tungsten oxide (WO.sub.3). Such film cooperates with a liquid electrolyte. A typical system of the second type ECD is disclosed in B. W. Faughnan et al, RCA Review 36 177 (1975).
Various driving systems are proposed for the electrochromic displays. The electrochromic displays inherently possess the memory characteristics, which maintains the colored state for several hours through several days after the applied voltage is removed.
Therefore, it is important to effectively use the above-mentioned memory characteristics in order to minimize the power dissipation of the driver circuit. Moreover, the display electrode must be placed in the completely bleached state while the display electrode is not placed in the coloration memory state.
In the case where the electrochromic display device includes a predetermined number of display segments, each of the various combinations of the display segments defining a different one of desired display patterns, non-selected display segments must be placed in the completely bleached state while the selected display segments are placed in the coloration memory state in order to enhance the display quality.